Make native_coverage clause work with ClangCoverage

Make uses NATIVE_COVERAGE to enable gcov coverage and CLANG_COVERAGE
to enable clang coverage.  NATIVE_COVERAGE is translated to the Soong
Native_coverage product variable which triggers the native_coverage
clause in Android.bp files.  The clause also needs to be triggered
for CLANG_COVERAGE.

Rename the existing Native_coverage product variable to GcovCoverage,
and regenerate Native_coverage when either GcovCoverage or
ClangCoverage are set.

Also remove NativeLineCoverage, it wasn't doing anything differently
than Native_coverage.

Bug: 159059537
Test: m checkbuild
Change-Id: I215124a9b35a2ad50ad562079d392e3d33da11f4

android/variable.go

@@ -270,12 +270,14 @@ type productVariables struct {
 	JavaCoveragePaths        []string `json:",omitempty"`
 	JavaCoverageExcludePaths []string `json:",omitempty"`
 
-	NativeLineCoverage         *bool    `json:",omitempty"`
-	Native_coverage            *bool    `json:",omitempty"`
+	GcovCoverage               *bool    `json:",omitempty"`
 	ClangCoverage              *bool    `json:",omitempty"`
 	NativeCoveragePaths        []string `json:",omitempty"`
 	NativeCoverageExcludePaths []string `json:",omitempty"`
 
+	// Set by NewConfig
+	Native_coverage *bool
+
 	SanitizeHost       []string `json:",omitempty"`
 	SanitizeDevice     []string `json:",omitempty"`
 	SanitizeDeviceDiag []string `json:",omitempty"`